Vacum Fiberglass Molding

And if the answer is yes, how come no manufacturer uses this particular method?,
Cost!

The thickness of each layer, or mat is known and the two mold halves are built to accommodate that thickness and give the desired finished thickness.

You could use this process to build boats, but the cost might be prohibitive. You also don't need two finished surfaces in most places in a boat, because they are not seen.

Use a vacuum bag, it's faster and cheaper.

I believe that I have seen a boat manufacturer use this technique before. I think it was on the Discovery channel. You will need a substantially high volume to justify cost investment.

Search Male/female prepregs.

This terminology is misleading, "Search Male/female prepregs."

Prepreg is the term used to identify glass cloth that has been impregnated with resin prior to placing the cloth into the mold. The cloth is supplied by the maker with the resin already in the cloth. This requires special handling and refrigeration due to the fact that the resin has been partially cured (B-staged)

"Fiberglass" (itself a misleading term) boats are usually made by a wet layup process.

Pangas are a great boat design, but aimed at the sensible utilitarian market. Many are chopper-sprayed into a mold, which is very low cost production resulting in a rough interior, and an exterior finish dependent on the quality of the mold and gel-coat, if any. Stiff market to penetrate without cheap labor, factory, materials. If you can build near the market, or make the design stackable like paper cups, transport might be a little cheaper. Where are you planning to build these boats?

Do not be confused between prepreg and glass/resin layup. They are very different puppies. Prepreg uses a fiber preform that is impregnated with a catalyzed resin matrix and then rapid cooled to inhibit curing. Some have UV accelerators in them so that the part can be irradiated prior to placing into an autoclave. VERY expensive, though Boeing have used this process for flexible leading edges up to 33ft long. What you see in the youtube video is a very different animal and bag molding would not work well with this part. Remember the operator poured resin into the bottom and yet the process brought the resin up the sides into a fairly consistent thickness. Try this with a bag and the wall thickness will vary greatly due to the bag moving the reinforcement and resin along in generally unintended directions. Certainly there are applications for bag molding but watercraft don't usually fall into that category. This "barrel" part is ideal for male/female molds with vacuum assist because; A) they are obviously not concerned with fiber strikethough to the surfaces, B) The lateral ribbing is on both the inside and outside. Yes you could include longitudinal ribbing for a boat but this process would make it difficult to add other moulded components later on with out extensive grinding away of the surface to be bonded to because of the type of release needed in this resin formulation. Think seats, transom, gunwales, thwarts, yoke, ballast and floatation pods, decks, etc. Notice also the stepping around the flange of the male mold. It is designed to draw the center part of the male mold down first, thus slowly displacing the resin puddle and then to draw any remaining air from within the fiber, thus ensuring more consistent wetting. P.S. don't try this with general layup resin. Talk to a "knowledgeable" resin supplier about the resin formulation if you do wish to go ahead. I am not ruling out bag molding or matched die molding, the both have their place, but there is chemistry and physics involved beyond the good old layup process. Good luck!

Hello,

My Name is Onnik Hovanessi, and I have just completed a Prototype Design for a Wind & Human Powered Water Craft, when I read about you factory and the manufacturing process, I wanted to drop you a line or two, that I am expressing interest to speak with you farther, and find out of what are your interests working in partnership with designers like myself. My Prototype design is fully functional at this time, yet in a first phase of being developed and need farther work to be market ready and show case exhibit design. Please let me know if you will be interested to farther consult with me for future partnership possibilities.

Thank you very much,

Onnik H.

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Some yacht builder do use this method for the yacht body. The method I have seen is to use a form for the outer surface and a LARGE plastic bag to cover everything. Since the bodies are so large they have to be careful to not get wrinkles in the plastic covering as the vacuum pulls the plastic tight over the form. Any vacuum pump will do. A larger pump will work faster. My best guess is that this use of a vacuum pump will wear it out quickly. You do not need a pump with a low base pressure but is does have to pull out all the air before the cure gets the fiberglass or epoxy too viscous. The builders I saw used epoxy with fiberglass cloth over a gel coat outer surface.

Thanks to all responders. I think some have not seen the video on the link i posted. I dont know why some believe i will use prepregs. Does the video suggest the use of prepreds?(exuse my ignorance, so lpease educate me). The link again is : http://youtu.be/MWUxhC6-q0c I thought of using the same technique using all the usual glass/matt layers and resin with the appropriate amount of hardner, all in one step, hoping the vacum will cause enought compression between the male and female molds to leave no air bubbles anywhere. And i thought this one step process would save a lot of time and energy compared to the conventional manuall multilayering.So why would it be more costly?..unless i am missing something? I am sure there are a lot of points and details the videao does not show, and although i did a lot of research, i could not find detailed information as to how to use this technique on boats. I would appreciate further clarification/elaboration.

The process is essentially the same with either technique. The difference is that you will have two "factory finished" sides to the molding using hard tooling on both sides..

All the mixing, pouring, layup and curing are the same. The difference is the cost of the second mold half as opposed to the cost of disposable vacuum bagging materials.

There is something to be said for the rough finish left by the bleeder cloth, especially on a boat.

Have you done this before?

I would expect (as several others have already mentioned) that costs may be too high.

Also I did not see much, other than the male moulding, that is vastly different to normal Fibre Glass working.

As someone else pointed out, not having a rough inner finish (that can be strongly bonded to, could be a minus. Gelcoat is not a strong bond and must be removed first) could be a possible liability in some areas.

Not forgetting stiffness and weight.

Boats generally, if an inner fibre glass gel coat finish is required use a second moulded insert that adds considerable strength and stiffness when bonded in correctly, also making some designs to some degree "double hulled" for floatational safety.

Some sort of foam can be used to fill the voids between hull and inner moulding and this would assist further in bonding the inner and the outer part to each other forever and a day......stiffer/safer/lighter and probably even cheaper to construct....as well as not requiring any guesswork on the voids, so can be made thinner/lighter.

I did not see any "real" dedicated prevention of voids in the video while laying up that could potentially make the finished unit potentially weak in certain critical areas. Whether or not this is critical to this particular design I could not say, but boats are very critical. Having both surfaces gel coated (or so it appears) means that optical (Mk.1 Eyeball!!) methods of finding and erasing voids, will be far more difficult, if not impossible.

Air trapped in the glass fibre layers is probably the single major cause of stress failures in some designs, especially in a heavily flexed area....rudder/mast/anchor/engine/fin areas....to name but a few.

If you cannot stop voids, the hull will need to be much thicker/stronger/heavier to make sure that sufficient strength is always achieved. The stiffness needed will generally also cost more in weight.....and let us not forget that weight is also a cost (the materials are not "cheap" anymore as they were say 40 years ago.....) and could be a performance factor in a boat.....

I personally see no pluses for boat hull construction where lightness/strength/stiffness/ease of construction/cost are most important...not necessarily in that order and maybe the list is incomplete as well!!

Yes you can use this technique and i have seen most of the manufacture also use this technique.

When I worked in the shipyard, we did a number of fiberglass boats normally 2 off designs.

Of which was multiple hulls.

we would do a 2-off design.

Basically make a finished plug of the actually hull. The we would make a mold of that, basically a reverse mold.

From that mold we would make the finished hull.

Now the first mold you may be able to get a few hulls off of that. we did have issues, and since it was for the U.S. Navy, there were a few hull that didn't meet MILSPEC that had to get rejected and had to redo it. Which was that bad becasue you still had the original plug design.